The field of plasmonics is capable of enabling interesting applications in different wavelength ranges, spanning from the ultraviolet up to the infrared. The choice of plasmonic material and how the material is nanostructured has significant implications for ultimate performance of any plasmonic device. Artificially designed nanoporous metals (NPMs) have interesting material properties including large specific surface area, distinctive optical properties, high electrical conductivity, and reduced stiffness, implying their potentials for many applications. This paper reviews the wide range of available nanoporous metals (such as Au, Ag, Cu, Al, Mg, and Pt), mainly focusing on their properties as plasmonic materials. While extensive reports on the use and characterization of NPMs exist, a detailed discussion on their connection with surface plasmons and enhanced spectroscopies as well as photocatalysis is missing. Here, we report on different metals investigated, from the most used nanoporous gold to mixed metal compounds, and discuss each of these plasmonic materials’ suitability for a range of structural design and applications. Finally, we discuss the potentials and limitations of the traditional and alternative plasmonic materials for applications in enhanced spectroscopy and photocatalysis.

Plasmonic nanocavities are able to engineer and confine electromagnetic fields into subwavelength volumes. In the past decade, they have enabled a large set of applications, in particular for sensing, optical...

However, due to the intrinsic low optical response of small objects, there has been a clear trade-off between the size of a material and its response to light. [5] Recently, plasmonic nanostructures have emerged as leading platforms to enhance the weak optical signals of low dimensional materials including quantum dots (QDs), [6] small molecules, [7,8] and 2D monolayers. [9] The plasmonic enhancement of linear and nonlinear optical processes capitalizes on the near-and far-field properties of metallic (e.g., gold and silver) nanostructures. [10] One of the defining features of plasmonic nanostructures is their potential to confine light into deep subwavelength volumes, which has opened a new door to trap and manipulate dielectric, metallic, and biological nano-objects. [11] Moreover, metallic nanostructures are characterized by their capability to amplify the intensity of optical fields by orders of magnitude. The enhancement of local field intensity is attributed to the resonance of plasmon polaritons arising from the coupling of external electromagnetic fields to the collective oscillations of the conduction electrons. [12] A small perturbation (or change in the refractive index) of the near field zone of plasmonic nanostructures leads to significant shift in the plasmon polariton resonance wavelength, which has important implications for surface-enhanced sensing and spectroscopic applications. [13,14] Thus, for the ad-hoc enhancement of optical Plasmonic nanocavities have proved to confine electromagnetic fields into deep subwavelength volumes, implying their potentials for enhanced optical trapping and sensing of nanoparticles. In this review, the fundamentals and performances of various plasmonic nanocavity geometries are explored with specific emphasis on trapping and detection of small molecules and single nanoparticles. These applications capitalize on the local field intensity, which in turn depends on the size of plasmonic nanocavities. Indeed, properly designed structures provide significant local field intensity and deep trapping potential, leading to manipulation of nano-objects with low laser power. The relationship between optical trappinginduced resonance shift and potential energy of plasmonic nanocavity can be analytically expressed in terms of the intercavity field intensity. Within this framework, recent experimental works on trapping and sensing of single nanoparticles and small molecules with plasmonic nanotweezers are discussed. Furthermore, significant consideration is given to conjugation of optical tweezers with Raman spectroscopy, with the aim of developing innovative biosensors. These devices, which take the advantages of plasmonic nanocavities, will be capable of trapping and detecting nanoparticles at the single molecule level.